This invention relates generally to magnetic disk data storage systems, and more particularly to magnetic write transducers and methods for making same.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIG. 1A and 1B, a magnetic disk data storage systems 10 of the background art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle S1 of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 (which will be described in greater detail with reference to FIG. 2A) typically includes an inductive write element with a sensor read element. As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to xe2x80x9cflyxe2x80x9d above the magnetic disk 16. Alternatively, some transducers, known as xe2x80x9ccontact heads,xe2x80x9d ride on the disk surface. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be written to and/or read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art.
FIG. 2A depicts a magnetic read/write head 24 including a substrate 25 above which a read element 26 and a write element 28 are disposed. Edges of the read element 26 and write element 28 also define an air bearing surface ABS, in a plane 29, which can be aligned to face the surface of the magnetic disk 16 (see FIG. 1A and 1B). The read element 26 includes a first shield 30, an intermediate layer 32, which functions as a second shield, and a read sensor 34 that is located within a dielectric medium 35 between the first shield 30 and the second shield 32. The most common type of read sensor 34 used in the read/write head 24 is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor.
The write element 28 is typically an inductive write element which includes the intermediate layer 32, which functions as a first pole, and a second pole 38 disposed above the first pole 32. The first pole 32 and the second pole 38 are attached to each other by a backgap portion 40, with these three elements collectively forming a yoke 41. The combination of a first pole tip portion 43 and a second pole tip portion 45 near the ABS are sometimes referred to as the yoke tip portion 46. A write gap 36 is formed between the first and second poles 32, 38 in the yoke tip portion 46. The write gap 36 is filled with a non-magnetic electrically insulating material that forms a write gap material layer 37. This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer 47 that lies below the second yoke 38 and extends from the yoke tip portion 46 to the backgap portion 40.
Also included in write element 28 is a conductive coil 48, formed of multiple winds 49 which each have a wind height Hw. The coil 48 can be characterized by a dimension sometimes referred to as the wind pitch P, which is the distance from one coil wind front edge to the next coil wind front edge, as shown in FIG. 2A. As is shown, the wind pitch P is defined by the sum of the wind thickness Tw and the separation between adjacent winds Sw. The conductive coil 48 is positioned within a coil insulation layer 50 that lies above the first insulation layer 47. The first insulation layer 47 thereby electrically insulates the coil layer from the first pole 32, while the coil insulation layer 50 electrically insulates the winds 49 from each other and from the second pole 38.
The configuration of the conductive coil 48 can be better understood with reference to a plan view of the read/write head 24 shown in FIG. 2B taken along line 2Bxe2x80x942B of FIG. 2A. Because the conductive coil extends beyond the first and second poles, insulation may be needed beneath, as well as above, the conductive coil to electrically insulate the conductive coil from other structures. For example, as shown in FIG. 2C, a view taken along line 2Cxe2x80x942C of FIG. 2A, a buildup insulation layer 52 can be formed adjacent the first pole, and under the conductive coil layer 48. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16 (see FIGS. 1A and 1B).
More specifically, an inductive write head such as that shown in FIGS. 2A-2C operates by passing a writing current through the conductive coil layer 48. Because of the magnetic properties of the yoke 41, a magnetic flux is induced in the first and second poles 32, 38 by write currents passed through the coil layer 48. The write gap 36 allows the magnetic flux to fringe out from the yoke 41 (thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS. A critical parameter of a magnetic write element is a trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by geometries in the yoke tip portion 46 (see FIG. 2A) at the ABS. These geometries can be better understood with reference to FIG. 2C. As can be seen from this view, the first and second poles 32, 38 can have different widths W1, W2 respectively in the yoke tip portion 46 (see FIG. 2A). In the shown configuration, the trackwidth of the write element 28 is defined by the width W2 of the second pole 38. The gap field of the write element can be affected by the throat height TH, which is measured from the ABS to the zero throat ZT, as shown in FIG. 2A. Thus, accurate definition of the trackwidth and throat height is critical during the fabrication of the write element.
Another parameter of the write element is the number of winds 49 in the coil layer 48, which determines magnetic motive force (MMF) of a write element. With increasing number of winds 49 between the first and second poles 32, 38, the fringing field is stronger and, thus, the write performance increases. The number of winds is limited by the yoke length YL, shown in FIG. 2A, and the pitch P between adjacent winds 49. However, to obtain faster recording speeds, and therefore higher data transfer rates, it may be desirable to have a shorter yoke length YL because this can shorten the flux rise time. This relationship can be seen in the graph of yoke length YL versus flux rise time shown in FIG. 2D. Therefore, to maximize the number of coil winds while maintaining fast write speeds, it is desirable to minimize the pitch P in design of write elements.
However, the control of trackwidth, throat height, and coil pitch can be limited by typical fabrication processes, an example of which is shown in the process diagram of FIG. 3. The method 54 includes providing a first pole with first and second edges in operation 56. This operation can include, for example, forming a plating dam, plating, and then removing the dam. In operation 58, a write gap material layer is formed over the first pole. In particular, the write gap material layer is formed over an upper surface and the first and second edges of the first pole. Also, in operation 58, a via is formed through the write gap material layer to the first pole in the backgap portion 40 (see FIG. 2A). In the instance herein described, the write gap material layer extends above the first pole in the area between the yoke tip portion and the backgap portion, although in other cases the write gap material layer may not be above this area. A buildup insulation layer is also formed in operation 60, adjacent the first and second edges, with the write gap material layer between the first pole and the buildup insulation layer. The buildup insulation layer is typically formed by depositing (e.g., spinning) and patterning photoresistive material and then hard baking the remaining photoresistive material. Such processes often result in the height of the buildup insulation layer being non-uniform and different than the height of the write gap material layer, as is illustrated in FIGS. 2A and 2C.
The method 54 also includes forming a first coil layer above the write gap material layer and the buildup insulation layer in operation 62. This can include first depositing a seed layer above the first pole. Typically, photoresistive material can then be deposited and patterned. With the patterned photoresistive material in place, conductive material can be plated. With removal of the photoresistive material, the remaining conductive material thereby forms the coil.
Unfortunately, when there is a difference in height between the write gap material layer and the buildup insulation layer, the patterning of the photoresistive material for the first coil layer can be complicated. In particular, it can be difficult to pattern the various heights to have consistent geometries. More specifically, winds of the resulting first coil layer can be wider at lower levels than at higher levels, such as between the first and second poles. Thus, for a given pitch, such greater width at the lower levels can result in smaller distances between winds. This can, in turn, result in electrical shorting between winds which can be detrimental to the write element performance. To avoid such electrical shorting, the minimum wind pitch can be set to a desired value that will result in adequate yield of non-shorting conductive coil layers. Because the coil winds are more narrow between the first and second poles, the resulting pitch there is typically greater than, and limited by this minimum. For example, typical wind pitches between the first and second poles may be limited to no less than about 3 microns. For a given number of winds and wind thickness, this in turn limits the minimum yoke length, and thereby limits the data transfer rate and data density as described above. For example, a pitch of about 3 microns may be adequate for recording densities on the order of about 2 Gb/sq.in., however, these typical pitches can be inadequate for larger recording densities, such as about 10 Gb/sq.in.
In operation 64, the method 54 further includes forming a coil insulation layer above the first coil layer that is formed in operation 62. In addition, in operation 66 a second pole is formed above the coil insulation layer of operation 64.
Still another parameter of the write element is the stack height SH, the distance between the top surface of the first pole 32 and the top of the second pole 38, as shown in FIG. 2A. Of course, this height is affected by the thickness of the first insulation layer 47, the thickness of the coil layer 48 and any other coil layers that might be included, and the height Hi of the coil insulation layer 50 and any other coil insulation layers that might be included. The stack height SH can be an indicator of the apex angle xcex1, which partially characterizes the topology over which the second pole must be formed near the yoke tip portion. Typically, the reliability of the write element decreases as the apex angle a increases. This is due, at least in part, to the corresponding increased difficulty, particularly in the yoke tip portion 46, of forming the second pole 38 over the higher topography of the stack. For example, the definition of the second pole width W, shown in FIG. 2C, including photoresist deposition and etching, can be decreasingly reliable and precise with increasing topography. When demand for higher density writing capabilities drives yoke tip portions to have smaller widths W, this aspect of fabrication becomes increasingly problematic.
In attempts to accommodate ever increasing data rate requirements, the above described design parameters are continually adjusted to the limits of available manufacturing capabilities. For example, yoke length YL must be shortened in order to minimize flux rise time. This means that the pitch P of the coil 48 must be minimized, requiring a reduction in wind thickness Tw accordingly. The reduction in wind thickness leads to a corresponding increase in electrical resistance in the winds 49.
Also, in order to minimize the yoke length YL, the number of winds 49 in a coil 48 must be reduced. However, with less winds available the current generated through the coil must be increased in order to maintain a sufficient magnetic motive force. This increase in current through the coil 48 along with the increased resistance of the winds 49, causes a dramatic increase in heat generation. The heat generated by the coil 48 during operation is defined by the formula W=I2R, where W is the amount of heat generated per second, I is the current flowing through the coil, and R is the electrical resistance of the coil.
The increased heat generated by a coil 48 of a high performance write element 28 degrades the performance of the read element 26. One reason for this decrease in performance is that the heat will cause thermal stresses on the read/write head 24 as the various materials expand at different rates. These thermal stresses will in turn cause magnetic domain motion in shield 32 which generates magnetic flux into read sensor 34. Due to magneto-resistive properties of the sensor, this undesired magnetic flux will be interpreted as a magnetic field. Another reason for this degradation of performance is that heat conducted to the read sensor 34 will cause xe2x80x9cJohnson Thermal Noisexe2x80x9d. xe2x80x9cJohnson Thermal Noisexe2x80x9d is proportional to (xcfx89)(KBT)(R) where xcfx89 is the frequency of the signal being read, KBT is the temperature of the sensor in degrees Kelvin and R is the resistance of the sensor.
Therefore, there remains a need for a high performance read/write head which can accommodate high data rate transfer while effectively dealing with increased heat generation. Such a read/write head would preferably experience negligible thermal interference in its read element, and would preferably not require an appreciable increase in manufacturing cost.
The present invention provides a magnetic write head, and a method for manufacturing same, having a structure for dissipating heat. The write head includes first and second magnetic poles joined at one end to form a yoke. A coil having a portion of its winds extending through the yoke imparts a magnetic flux through the yoke when an electrical current is caused to flow through the coil. The coil sits upon a layer of dielectric, thermally conductive material, which conducts and dissipates heat generated by the coil.
The preferred embodiment of the present invention includes a read element and a write element combined to form a combination read/write head, all of which is built upon a ceramic substrate. The read portion of the head includes a read sensor embedded within a first dielectric layer. This first dielectric layer is sandwiched between a first and a second shield.
The second shield of the read element serves as a portion of the first pole of the write element. The second shield/first pole has a flat upper surface, from which extends a write gap pedestal and a back gap pedestal. A second dielectric layer is formed over the first pole, and is planarized by a chemical mechanical polishing process. The polishing process exposes the flat upper surfaces of the pedestals and creates a smooth planar surface across the pedestals and the dielectric layer. The second dielectric layer is constructed of an electrically insulating, thermally conducting material, and extends laterally across the substrate beyond the first pole to provide an effective heat sink.
Upon the smooth surface of the second dielectric layer the coil is formed, including a pair of contacts at the inner and outer ends of the coil. An insulation layer is deposited over the coil and formed so as to not cover the back gap or write gap pedestal. In addition, the insulation layer is formed with openings called xe2x80x9cviasxe2x80x9d at the location of the contacts of the coil. A thin layer of electrically insulating, non-magnetic material is then deposited over the insulation layer and over the write gap pedestal. Again, the write gap material is formed so that it does not cover the back gap pedestal or the contacts of coil, although it does cover the write gap pedestal.
To complete the read/write head, the second pole is formed over the first pole. The back of the second pole contacts the back gap pedestal of the first pole, and the front of the second pole sits atop the write gap material above the write gap pedestal of the first pole.
In use, when a voltage is applied to the contacts of the coil, a current will flow through the coil. This current will generate heat according to the formula W=I2R, where W is the heat generated per second, I is the current flowing through the coil, and R is the resistance of the coil. The heat generated by the coil will flow through the thermally conductive second dielectric layer. The heat will be conducted out of the yoke through this dielectric layer and dissipated so that it will not affect the read performance of the read/write head.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings.